Hybrid electromechanical-semiconductor circuit breaker



Dec. 9, 1969 n. L. NEILL 3,433,432

HYBRID ELECTROMECHANICAL-SEMICONDUCTOR CIRCUIT BREAKER Filed Dec. 13, 1966 2 Sheets-Sheet 1 FIGI INVENTQR DANIEL L. NEILL WW W MZMW ATTORNEYS Dec. 9, 1969 o. L. NEILL 3,483,432

HYBRID ELECTROMECHANICAL'SEMICONDUCTOR CIRCUIT BREAKER Filed Dec. 13. 1966 2 Sheets-Sheet 2 o +28 VDC FIG I INVENTOR DANIEL L. NEILL ATTORNEY! United States Patent 3,483,432 HYBRID ELECTROMECHANICAL-SEMICONDUC- TOR CIRCUIT BREAKER Daniel L. Neill, Jackson, Mich., assignor to Howard Aiken Industries, Inc., Carlisle, Pa., a corporation of Delaware Filed Dec. 13, 1966, Ser. No. 601,360 Int. Cl. H02h 1/00; H01h 47/00, 7/03 U.S. Cl. 317-58 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker including two solenoids having a common core plunger movable between a trip position and a set position in accordance with the energization of the solenoids, a bistable snap action switch actuated by the plunger between a stable trip position and a stable set position, and a pneumatic dashpot for retarding movement of the switch to one of the positions.

This invention relates generally to remotely controlled circuit breakers and more particularly to an improved hybrid electromechanical-semiconductor circuit breaker.

Broadly the invention is an improved remotely controlled circuit breaker incorporating a solenoid-actuated bistable snap blade for load switching and solid state circuits for trip and reset control. The snap blade is actuated by a plunger which serves as a common movable core for trip and reset solenoids mounted on opposite sides of the snap blade. In the normal set or closed position of the circuit breaker, the load is energized through the snap blade and a pair of contacts mounted on opposite ends thereof. When a trip signal from a load sensing circuit is applied to the trip control circuit, the trip solenoid is energized to actuate the snap blade to its trip position in which the load is interrupted at both contacts. A reset signal must then be applied to the reset control circuit to energize the reset solenoid to reset or reclose the circuit breaker, i.e. return the snap blade to its normal position so that the load is energized.

In the set or closed position of the circuit breaker, closed control contacts connect a control voltage supply and the trip solenoid to a normally non-conducting silicon controlled rectifier. When a trip signal is applied to the gate of the SCR, the SCR fires and the trip solenoid is energized to actuate the snap blade to the trip or open position. In the trip position, the control contacts of the trip solenoid are opened and another set of control contacts are closed to connect the reset solenoid and control voltage supply to another non-conducting SCR. When a reset signal is applied to the gate of the second SCR, the reset solenoid is energized to actuate the snap blade to its normal position to close the load circuit, open the reset control contacts, and close the trip control contacts. The trip control may also be energized manually to open the load circuit at any time. Auxiliary contacts on the snap blade permit an appropriate trip indicator to be energized when the snap blade is in its trip or open position.

Once the SCR in the trip solenoid circuit is fired, no additional trip signal is required to maintain the circuit breaker in the tripped condition. The same is true when the SCR in the reset solenoid circuit is fired to reset the circuit breaker. The incorporation of the snap blade in such a hybrid circuit breaker eliminates the necessity for standby power once the circuit breaker is placed in either its trip or set position.

The bistable snap blade is a monometal, rather than a bimetal, and is preferably dish-shaped even though other forms of snap blades may be used. The plunger and aux- 3,483,432 Patented Dec. 9, 1969 "ice .iliary contacts are spring mounted. The plunger, which acts as the snap blade actuator and as the movable core for the trip and reset solenoids, includes an integral pneumatic dashpot which retards the closing or resetting move ment of the plunger to damp out vibration and eliminate contact chatter without inhibiting the quick tripping or opening action of the breaker.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a cross-section view showing the structure of an improved hybrid electromechanical-semiconductor circuit breaker;

FIGURE 2 is a schematic diagram of the improved circuit breaker; and

FIGURE 3 is a schematic diagram showing a modified trip and reset control circuit for the improved circuit breaker.

In FIGURE 1, a preferred embodiment of the improved hybrid electrornechanical-semiconductor switch 10 is shown enclosed in a housing 12. A semiconductor load current sensing circuit 14 which produces a trip signal upon the occurrence of an overload is the subject of another patent application.

In the illustrated embodiment, switch 10 includes a bistable monometal snap blade 16 which is a dish-type blade in the preferred embodiment, but may be a slotted springtype, for example. In FIGURE 1, the switch is shown in its set or closed position in which the movable switch load contacts 18 and 20 are in engagement with the fixed load contacts 22 and 24, respectively. Fixed load contact 22 is mounted on a pin 26 which passes through the base 28 of housing 12, and fixed load contact 24 is fixed to a pin 30 which also passes through base 28. In use, pins 26 and 30 are connected in series with the load to be protected.

A reset solenoid 32 is mounted at the top of housing 12, and a trip solenoid 34 is mounted on the base 28. A magnetic core plunger 36 acts as a movable armature for the two solenoids and also passes through and is secured to, snap blade 16. In the set condition illustrated, plunger 36 is in its upper position, and snap blade 16 is also in its upper flexed position. A control contact 38 mechanically fixed to plunger 36, but electrically isolated therefrom, is in engagement with a control contact 40 which is mounted on a piston 42. Piston 42 is spring biased downwardly by means of a spring 44. The enlarged upper portion 46 of plunger 42 extends into a small cylinder 48 formed in housing 12. Cylinder 48, piston 42 and spring 44 act as a dashpot to damp out vibrations of contact 40 when it is forceably engaged by contact 38, upon resetting of the breaker.

In like manner, another control contact 50 is also fixed to plunger 36. Contact 50 is disposed opposite a corresponding control contact 52 fixed to a plunger 54 which is spring-mounted by a spring 56. Plunger 54 cooperates with a cylinder 58 to form a dashppt in the manner described in connection with contact 40.

Control contact 40 is connected through a solid state trip control circuit 60 and trip solenoid 34 to pins 62 and 63. The internal trip signal from the trip control system 14 appears on pin 62 for monitoring. Pin 63 is connected to an external remote trip control which may be manually actuated, from the cockpit of an airplane, for example. In like manner, the control contact 52 is electrically connected through a solid state reset control circuit 64 and reset solenoid 32 to pin 66.

Mounted on snap blade 16 opposite contacts 18 and 20 are contacts 68 and 70, respectively. Opposite contact 68 is an auxiliary contact 72 mounted on a member 74 which is spring-mounted on an arm 76 by a Spring 78. Arm 76 is fixed to housing 12 and extends through base 28 as a pin 80. In like manner, another auxiliary contact 82 is mounted opposite contact 70 and is fixed to a member 84 which is spring-mounted on an arm 86 by means of a spring'88. Ann 86 is fixed to housing 12 and extends through base 28 as another pin 89. When the switch is in its set or closed position, as illustrated, auxiliary contacts 68, 72 and 70, 82 are open. However, when plunger 36 is moved downwardly to cause snap blade 16 to flex so that contacts 68 and 70 move upwardly to place the switch in its open or trip position, these auxiliary contacts are then closed. Pins 80 and 89 may be connected to any appropriate trip indicator means.

A set reaction spring '90 is mounted in the bore of reset solenoid 32 and biases plunger 36 downwardly. In like manner, a trip reaction spring 92 is mounted in the bore of trip solenoid 34 and biases the plunger 36 upwardly. However, the force produced by set reaction spring 90 exceeds the force of the trip reaction spring 92 by a considerable amount (about 24 ounces minimum) to produce adequate contact forces for a 50 ampere rating, for example. Since the auxiliary contacts do not require such high forces, trip reaction spring 92 can have a much lower spring constant than set reaction spring 90. Auxiliary contact springs 78 and 88 compensate for the lighter trip reaction spring 92. The mass-spring system formed by the components of the switch is susceptible to vibration in the plane normal to the axis of plunger 36. In order to eliminate this vibration, the reset solenoid 32 and the trip solenoid 34 are designed to cooperate with plunger 36 to form a unidirectional dashpot. The upper portion 100 of plunger 36 is reduced in diameter so that there is a slight clearance between portion 100 and the inner surface of the bore of reset solenoid 32. In like manner, the lower portion 102 of plunger 36 is reduced in diameter so that a small gap is formed between it and the inner surface of the bore of trip solenoid 34. An axial bore 104 extends the length of plunger 36. A spring -biased check ball valve 106 mounted in the plunger adjacent the upper end of bore 104 provides the unidirectional damping feature. Check valve 106 permits rapid downward movement of plunger 36 to trip the breaker but tends to delay or inhibit upward motion of plunger 36 upon closing or setting of the switch contacts. This dashpot effect prevents contact chatter or vibration which otherwise might occur because of the characteristic susceptibility of the plunger mass-spring system to vibrate, and uncontrolled sympathetic vibration is positively inhibited.

FIGURE 2 is a schematic diagram of the electrical circuit of the improved hybrid electromechanical-semiconductor switch, the structure of which is illustrated in FIGURE 1. Where appropriate, the same reference n-umerals have been used in FIGURES 1 and 2 to identify the corresponding parts.

A silicon controlledrectifier 110 is connected in series with trip solenoid 34, control contacts 38 and 40, and a lead 112 which is connected to 21 +28 v. DC control voltage supply in this example. The gate 114 of SCR 110 is connected through a capacitor 116 to the trip signal input pin 62. Gate 114 is also connected through another capacitor 118 which extends to the remote trip signal input pin 63. A resistor 122 is connected between gate 114 and ground. In like manner, an SCR 124 is connected in series with reset solenoid 32, control contacts 50, 52 and a lead 126 which is also connected to the DC control voltage. The gate 128 of SCR 124 is connected through a capacitor 130 to the reset pin 66. A resistor 132 is connected between the gate and ground.

In operation, when snap blade 16 is in its set or closed position illustrated by the full lines in FIGURE 2, a load connected between pins 30 and 26 is energized through contacts 22 and 18, switch blade 16, and contacts 20 and 24. In this position, control contacts 38and 40 are closed, but control contacts 50 and 52 are open. Consequently, SCR 110 is forward biased by the +28 v. DC applied to lead 112. However, SCR, 110 is held non-conducting by gate 114 in this switch position when rated load current is flowing. However, upon the occurrence of an overload current, a positive trip signal derived from sensing system 14 is-applied to pin 62 through capacitor 116 which applies a firing pulse to gate 114. Consequently, SCR 110 becomes immediately conducting to complete a current path through trip solenoid 34. Solenoid 34 is thereby energized to attract plunger 36 downwardly against the force of trip reaction spring 92. (See FIG- URE 1.) Once snap blade 16 passes over center, it snaps into the dotted line position shown in FIGURE 2 and requires no standby electrical power to maintain it in that position. The difference in spring constants between springs and 92 aids in the mechanical action of the snap blade in keeping the blade in its trip position.

When the blade snaps to its tripped position, trip control contacts 38 and 40 open to interrupt the current through SCR and return the SCR to its non-conducting state. Simultaneously control contacts 52 and 50 are closed to forward bias SCR 124 by virtue of its connection through reset solenoid 32, to lead 126 which is connected to +28 v. DC control voltage. If it is desired to reset or reclose the circuit breaker 10, a positive reset voltage is applied to pin 66 and converted to a pulse by means of capacitor 130. The outputof capacitor is applied to gate 128 and fires SCR 124 so that current flows through reset solenoid 32, thereby energizing the solenoid and attracting plunger 36 upwardly so that snap blade 16 is returned to its initial set or load energizing position. Again, no standby electrical power is required to maintain the bistable snap blade 16 in this stable set position. The reset signal applied to pin '66 must be at least 1.0 volt DC in order to fire SCR 124.

Capacitor 130 serves two functions. It converts a voltage level to a pulse to fire SCR 124, thereby eliminating the necessity for standby power consumption. In addition, capacitor 130 prevents recycle closing of the circuit breaker after overload tripping. Thebreaker cannot be reset until the reset signal is removed and then reapplied. When the reset signal is removed capacitor 63 discharges through resistor 132. The input impedances of the trip and reset control circuits 60 and 64 are kept low to insure compatibility of the electromechanical and solid state components and also to reduce noise and transient susceptibility of the trip and reset triggering circuits.

Also illustrated in FIGURE 2 is a modification of the trip and reset control circuits 60 and 64. An additional circuit 136 may be connected between the reset signal pin 66 and the trip signal pin 62. Circuit 136 includes an NPN transistor 138 having its collector connected through a load resistor 140 to the +28 V. DC. control voltage and also to the trip input lead 62. The base of transistor 138 is connected through a voltage divider 142, 144 to reset pin 66. The emitter of transistor 138 is connected to ground. Located remotely from the circuit breaker are a switch 145 and a trip indicator lamp 146. Lamp 146 is connected to one of the auxiliary contacts 72 or 82 and is energized by +28 v. when the circuit breaker is tripped.

In the operation of this modification, a continuous reset signal of approximately 1 milliwatt is applied to pin 66 from remote switch 145 to maintain the circuit breaker in set or closed position. The cessation of such a signal would then permit the breaker to open or trip. No power would be consumed duringthe time the load circuit was open. The primary benefit of this modification is the reduction of necessary control wires to the circuit breaker from two wires to one wire. However, one additional wire is required to bring the trip indication from the auxiliary contacts to indicator 146.

More specifically, if the breaker illustrated in FIGURE 2 is assumed to be in its trip position illustrated by the dotted lines, an application of a positive reset signal to pin 66 will fire SCR 124 and energize the reset solenoid 32 to reset the breaker. The reset signal is continuously applied so that transistor 138 is conducting, and its collector voltage applied to pin 62 is substantially at ground, and well below the minimum trip signal level. When the resetsignal is removed, transistor 138 is cut off and its collector rises to the control voltage of +28 volts D.C. The resulting positive-going voltage is coupled through capacitor 116 to the gate 114 of SCR 110 and fires the SCR to energize the trip solenoid 34 and trip the breaker. When the breaker is closed, any overload current will actuate the overload sensing system 14 to produce the trip signal which is applied to pin 62 to trip the breaker as previously described.

Still another modification of the trip and reset control circuit is shown in FIGURE 3. This arrangement requires only one wire between the circuit breaker and a remote single pole, double throw-actuator switch 147 and a remote indicator 148 to provide both control and indication functions. The same reference numerals are used for identical parts of FIGURES 2 and 3.

In FIGURE 3, when load contacts 20 and 24 are open, a switch transistor 150' obtains power from the +28 v. D.C. control bus through collector resistor 152, winding 32, and closed contacts 50, 52. The transistor is biased on by a resistor 154, thereby effectively shorting to ground the base of another transistor 149. Consequently, transistor 149 is off. The reset terminal 66 and trip terminal 62 are connected in common to the emitter of transistor 149, the emitter being connected through a resistor 156 to ground. With transistor 149 turned off, terminals 62 and 66 are esesntially at ground potential. The +28 v. D.C. control bus potential is applied through terminal 80, the auxiliary contacts 72 and 82, terminal 89 and a resistor 158 to a single remote control wire 164. Indicator 148 and switch 147 require only ground connections at the remote location, thus eliminating the need for additional protective means for wire 164 which may be shorted to ground without endangering any power bus connections.

In the operation of this modification, switch 147 is in the center position with both contacts 160 and 162 open when the load contacts 20, 24 are open as illustrated by the dotted line position of blade 16. Control contacts 50, 52 are closed and contacts 38, 40 are open. To close the load contacts, ground is placed on wire 164 by throwing switch 144-so as to close contact 160. This shorts the base of transistor 150 to ground turning it off. Diode 168 insures that junction 170 will be 'at a voltage lower than necessary to forward bias transistor 150 into conduction. Transistor 149 now is forward biased and becomes conducting to raise the potential at terminals 66 and 62 to approximately volts. This voltage transition is coupled to the gate of SCR 124 through capacitor 130 to fire SCR 124, thereby energizing reset solenoid 32 to reset the breaker. SCR 110 is not affected as control contacts 38, 40 remain open until reset actually occurs. Switch147 is then thrown to close contact 162 and prepare a circuit to indicator 148. If a trip signal should occur at terminal 63, SCR 110 will fire, thereby energizing trip solenoid 3'4 and causing the load contacts to open as the auxiliary contacts 72, 82 are closed through blade 16. This tripped condition will be indicated by the circuit from the +28 volts D.C. control bus through the contacts 72 and 82, resistor 158, wire 164 and contact 162 of switch 147. Diode 166 prevents transistor 149 from shorting indicator 146. The breaker may be reset by throwing switch 47 to contact 160 which repeats the process previously described.

It the breaker had not tripped with switch 147 closed to contact 162, the breaker couldhave been manually opened by throwing switch 144 to contact 160, to turn off transistor 150 and turn on transistor 149, thereby producing a positive pulse at terminals 62 and 66. In this case, the pulse fires SCR 110 to open the breaker since control contacts 38, 40 were closed and contacts 50, 52 were open.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A circuit breaker comprising:

(a) a housing,

(b) a first solenoid mounted on said housing,

(c) a second solenoid mounted on said housing,

(d) a common core plunger for said solenoids and movable between a trip position and a set position in accordance with the energization of said solenoids,

(e) a bistable snap action switch means coupled to and actuated by said plunger, one stable position of said switch corresponding to the trip position and the other to the set position, and

(f) a pneumatic dashpot at one end of said plunger for retarding movement of said switch means to one of the stable positions.

2. A circuit breaker as defined in claim 1 wherein said pneumatic dashpot comprises:

(a) a cylinder formed in one of said solenoids, and

(b) a piston formed on one end of said plunger and disposed within said cylinder. 7

3. A circuit breaker as defined in claim 2 wherein said dashpot retards the movement of said switch means in only one direction and said plunger has an axial bore extending the length thereof, and further comprising a check valve mounted in said bore to permit fluid flow therethrough in only one direction.

, 4. A circuit breaker as defined in claim 3 further comprising:

(a) first spring means biasing said plunger towards its set position, and

(b) second spring means biasing said plunger toward its trip position, said first spring means exerting a substantially stronger bias force than the other.

5. A circuit breaker as defined in claim 1 further comprising:

(a) a pair of load contacts mounted on said switch means,

(b) first and second control contacts mounted on said switch means, and

(c) third and fourth control contacts spring mounted relative to said housing, and each adapted to be engaged by a different one of said first and second control contacts, said first and third control contacts being in engagement in the set position and said second and fourth control contacts being in engagement in the trip position.

6. A circuit breaker as defined in claim 5 further comprising:

(a) a solid state trip control circuit mounted on said housing and electrically connected to said first solenoid, and

(b) a solid state reset control circuit mounted on said housing and electrically connected to said second solenoid. I

7. A circuit breaker as defined in claim 6 further comprising:

(a) first conductor means connecting in series said first and third control contacts, said first solenoid, and said trip control circuit,

(b) second conductor means connecting in series said second and fourth control contacts, said second solenoid and said reset control circuit, and

(0) input means for applying control signals to said trip and control circuits to complete current paths through said first and second solenoids, respectively, to actuate said switch means to its trip and reset bistable positions, respectively.

8. A circuit breaker as defined in claim 7 wherein each of said control circuits comprises:

(a) a solid state controlled rectifier having its anodecathode circuit connected in series with its associated solenoid, and

(b) means connecting the gate of each rectifier to said input means.

9. A circuit breaker as defined in claim 8 wherein said switch means further comprises:

(a) a conductive bistable blade,

(b) first and second auxiliary contacts mounted on opposite ends of said blade, and

(c) third and fourth auxiliary contacts spring mounted on said housing and adapted to be engaged by said first and second auxiliary contacts, respectively, when said switch means is in the trip position.

10. A circuit breaker as defined in claim 9 wherein said input means conprises:

(a) a trip terminal connected to said trip control circuit,

(b) a rest terminal connected to said reset control circuit, and

(c) a normally conducting transistor connected between said trip and reset terminals for applying a control signal to said trip control circuit when said transistor is cut off.

11. A circuit breaker as defined in claim 10 further comprising means connecting said transistor to a first source of control power whereby said control signal is shunted away from said trip terminal when said transistor is conducting.

12. A circuit breaker as defined in claim 11 further comprising:

(a) a remote actuator switch,

(b) means connecting one side of said actuator switch to a second source of control power, and

(c) means connecting the other side of said switch to the base of said transistor and to said reset terminal.

13. A circuit breaker as defined in claim 12 further comprising a remote trip indicator connected between said other side of said switch and one of said auxiliary contacts, whereby said trip indicator is energized from said second source of control power when said circuit breaker is in the trip position.

14. A circuit breaker as defined in claim 9 further comprising:

(a) a trip terminal connected to said trip control circuit,

(b) a reset terminal connected to said reset control circuit,

(c) a trip indicator and a single pole, double throw actuator switch located remotely from said switch means, said actuator switch having a movable element and two fixed contacts,

(d) a single wire having its remote end connected to said movable element and its local end to one of said auxiliary contacts,

(e) means for connecting another of said auxiliary contacts to a source of voltage, and 7 (f) means connecting said trip indicator across said two fixed contacts of said switch actuator.

15. A circuit breaker as defined in claim 14 further comprising:

(a) means connecting one of said fixed contacts to ground, I

(b) a first transistor connected between said second conductor means and ground,

(c) means connecting the base of said first transistor to the local end of said single Wire so that said first transistor is conducting when said circuit breaker is in the trip position,

(d)a second transistor coupled between said second conductor means and ground,

(e) a resistor connected between ground and the emitter of said second transistor,

(f) means connecting the base of said second transistor to the collector of said first transistor so that said second transistor is non-conducting when said circuit breaker is in the trip position, and

(g) means connecting said trip and reset terminals to the junction of said resistor and the emitter of said second transistor, so that the engagement of said movable element with the grounded fixed contact renders said first transistor non-conducting to render said second transistor conducting, thereby applying a control signal to said reset control circuit to place said circuit breaker in the set position, and so that the subsequent engagement of said movable element with the other fixed contact of said actuator switch causes said indicator to be energized from said voltage source when the circuit breaker is subsequently returned to its trip position.

References Cited UNITED STATES PATENTS 1,582,987 5/1926 Hart 335- 2,335,888 12/1943 Stilwell 335-180 XR 2,544,719 3/1951 OBrien et al 335-180 2,738,395 3/1956 Reihman 335-180 XR 2,841,669 7/1958 Cook 335-180 XR 2,919,324 12/1959 Schuessler 335-180 XR 3,170,095 2/1965 Goldstein 317-1555 3,214,644 10/1965 McCoy 317-1485 3,304,444 2/1967 Smith 307-112 3,384,790 5/1968 Holec 317-1485 LEE T. HIX, Primary Examiner W. M. SHOOP, JR., Assistant Examiner US. Cl. X.R. 

